// Symbol is a primitive value in that it cannot be mutated
let s1 = Symbol();
let s2 = Symbol();

console.log (s1, s2, s1 === s2);

// Symbols in Object

let obj = {
    prop: 123,
    [Symbol("identifier")]: "foo"
}
let sym = Symbol(123)
obj[sym] = 234;


console.log(Object.keys(obj)); // ["prop"]
console.log(Reflect.ownKeys(obj)); // ["prop", Symbol(identifier)]
console.log(obj[sym]); // 234